The announcement came as Brussels -- home to the EU and NATO -- and other European capitals were on high alert over the threat of attacks during the New Year holiday.
The Belgian national, identified only as Ayoub B., was detained on Wednesday during a raid on a house in the troubled Brussels neighbourhood of Molenbeek, a statement from the federal prosecutor's office said.
He has been charged with "terrorist murder" and involvement in the activities of a terrorist group, it said, adding that he will appear in court again within five days for a custody hearing.
Molenbeek is home to the Paris attacks fugitive Salah Abdeslam and has emerged as a European hotbed of Islamist extremism.
Belgian authorities on Wednesday cancelled annual New Year's Eve celebrations and fireworks in the heart of Brussels after revealing an alleged jihadist plot to strike "emblematic sites" in the capital during the festivities.
Two men arrested over the plot were to appear in court on Thursday.
A source close to the investigation told AFP that officials were trying to determine whether members of a motorcyle gang called the "Kamikaze Riders" were involved.
Belgian media said the gang's founder was one of the two held.
Brussels has been on high alert since it emerged that several of the attackers involved in the Paris carnage on November 13 had links to the city of 1.2 million people.
The city's mayor Yvan Mayeur announced Wednesday that fireworks and other celebrations had been cancelled.
It said that in the current circumstances it was not possible to "guarantee that we can check everyone coming to the event".
"It's better not to take any risks," he added.
Last year, some 100,000 people turned out to watch the traditional New Year's Eve fireworks display at the central Place de Brouckere.
Speaking for the first time since the attack plot was revealed, Belgian Prime Minister Charles Michel said the decision to cancel the festivities was a tough one but the right one.
"It was, I understand well, a delicate, difficult decision for the mayor to take," Michel said.
It is not however the first time the New Year's Eve fireworks have been cancelled as the authorities made the same decision in 2007 because of another terror threat.
Officials said the plot disclosed Tuesday was not directly linked to the wave of bombings and shootings on a Paris concert venue, bars, restaurants and the national stadium that left 130 people dead and many more wounded.
The fugitive suspect Abdeslam is believed to have fled to Brussels in the hours after the attacks, which were claimed by the Islamic State jihadist group.
The French capital also remains on high alert and has abandoned its fireworks display on the Champs-Elysees, although the traditional gathering on the famous boulevard will go ahead under tight security.